Twenty-six people are in hospital following the chemical alert at a Twickenham school today, the ambulance service said.

A spokesman for the London Ambulance Service said: "We were called at 10.36am to reports of a chemical leak at St Catherine's School, Twickenham.

“We sent two single responders in cars, eight ambulance crews, the hazardous area response team and two managers.

“Our staff treated 26 patients for minor symptoms, such as coughing and sore throats, and took them to hospital.

"Nine patients were taken to West Middlesex, three to Ealing, six to St George's and eight to Kingston Hospital.”

The school's caretaker was one of the patients taken to hospital.

He was back working at the school this afternoon, headteacher Sister Paula Thomas confirmed.

A fire official earlier confirmed engineers caused the chemical reaction which led to the mass evacuation of the school.

Fourteen fire engines and nearly 20 ambulances were called to St Catherine's School in Cross Deep at about 10.52am following reports of chemical leak.

It later emerged the incident was caused by contractors who were working in the swimming pool area of the school.

The chemicals mixed as old cleaning equipment for the pool was removed and a new system put in resulting in a chemical reaction.

Simon Brownings, Kingston station manager, said: "We were called to a suspected chemical leak at the school.

"Crews very quickly ascertained what it was and what had happened.

"There are contractors working at the school and unfortunately they mixed the chemicals together and caused a reaction in one of the drains."

More than 150 children were at the school attending the Barracudas Summer Activity Camp.

They were evacuated and taken to St James' Independent School for Boys opposite for safety.

They returned to St Catherine’s just after noon when the all-clear was given by the fire brigade.

Pope’s Grove was cordoned off by police while fire crews dealt with the incident.

It has now been reopened.

Did you see what happened? Call the newsroom on 020 8744 4272 or email jkilvington@london.newsquest.co.uk.